In order to meet growing demands for higher-performance engineering plastics, attempts have been made to improve characteristics of thermoplastic resin materials. For example, Polymer, 26, 1855(1985) describes the compounding of an elastomer component into nylon 66 wherein the elastomer component is finely dispersed so that a high impact strength is achieved. It is also known that the heat resistance or the rigidity of a resin material can be enhanced by adding an inorganic filler into the resin material. However, such an improvement in one characteristic by quality reforming is often accompanied by deterioration in another characteristic. For example, if an elastomer component is added to a material to improve impact strength or ductility, the heat resistance or rigidity of the material deteriorates. Conversely, if various inorganic fillers or reinforcing agents are compounded into materials to improve heat resistance or rigidity, the ductility of the material, such as Izod impact strength, tensile elongation, surface impact strength and the like, deteriorates. Therefore, it is difficult to improve the impact strength or ductility and the rigidity of a material at the same time.
It is also known that the compounding of a fibrous reinforcing material, such as glass fiber, improves rigidity and also notched Izod impact strength. In this known method, however, surface impact strength and notch-less Izod impact strength deteriorate in comparison with a non-reinforced material. Furthermore, the reduced elongation of the material or the influence of the orientation of the fibrous reinforcing material gives rise to problems of anisotropy in mechanical characteristics, warping or the like. Thus this method has adverse effects on engineering materials as well.
Various considerations have been made as to how to control or curb decreases in the impact strength or tensile elongation that occur if an inorganic filler, other than fibrous materials, is added to a resin material. For example, Japanese patent application laid-open No. Sho 61-36340 discloses a method in which glass beads are coated with at most 1% by weight of a coating material such as a silane compound, a fluorocarbon compound or the like. However, although the coated glass beads control the decrease in impact strength compared with materials containing non-coated glass beads, the impact strength of the materials containing coated glass beads is still lower than that of the materials containing no filler. In addition, it has been found that the disclosed method does not achieve sufficiently high tensile rupture elongation or sufficiently high surface impact strength.
Japanese patent application laid-open No. Sho 62-253652 discloses the melt-kneading of a resin, such as a polyphenylene-based resin, which has a high glass transition temperature, and a rubber-like polymer, unsaturated carboxylic acid together with polyamide for the purpose of achieving both a good impact resistance and a good heat resistance. However, this technology has drawbacks of insufficient heat resistance and insufficient dimensional stability. If an inorganic filler is merely added to overcome the drawbacks, there results considerable deterioration in impact resistance, high-speed surface impact fracture characteristic and tensile elongation, thus failing to provide a material with sufficiently improved characteristics.
The present invention relates to a polyamide resin composition that is excellent in rigidity and toughness and particularly excellent in tensile elongation, and high-speed surface impact fracture characteristic, and that achieves excellent surface external appearance and dimensional stability of formed articles in good balance. This invention also relates to a method for producing the polyamide resin composition, and articles formed from the polyamide resin composition.
According to a first aspect of the present invention, there is provided a polyamide resin composition substantially composed of (A) nylon resin, and (B) at least one of a non-fibrous inorganic filler having an average particle diameter of 0.05-10 xcexcm and a fibrous inorganic filler, excluding glass fiber, having a fiber diameter of 0.05-10 xcexcm is melt-kneaded together with the nylon resin (A), in a compounding amount of 5-150 parts by weight relative to 100 parts by weight of the nylon resin (A). The amount of a polyamide resin component deposit remaining on the inorganic filler when the inorganic filler is recovered by dissolving the polyamide resin composition into hexafluoroisopropanol is at least 4 g/m2 per unit surface area of the inorganic filler measured by a BET method.
According to another aspect of the present invention, there is provided a method for producing a polyamide resin composition, wherein (A) 100 parts by weight of nylon resin, and (B)5-150 parts by weight of at least one of a non-fibrous inorganic filler having an average particle diameter of 0.05-10 xcexcm and a fibrous inorganic filler, excluding glass fiber, having a fiber diameter of 0.05-10 xcexcm are melt-kneaded, in such a manner that an amount of a polyamide resin component deposit remaining on the inorganic filler when the inorganic filler is recovered by dissolving the polyamide resin composition into hexafluoroisopropanol becomes at least 4 g/m2per unit surface area of the inorganic filler measured by a BET method.
According to still other aspects of the present invention, there are provided vehicle exterior parts, an under-hood part foaming for a motor vehicle, and a portable device casing which are formed from a polyamide resin composition substantially composed of (A) nylon resin, and (B) at least one of a non-fibrous inorganic filler having an average particle diameter of 0.05-10 xcexcm and a fibrous inorganic filler, excluding glass fiber, having a fiber diameter of 0.05-10 xcexcm which is melt-kneaded together with the nylon resin (A), in a compounding amount of 5-150 parts by weight relative to 100 parts by weight of the nylon resin (A). An amount of a polyamide resin component deposit remaining on the inorganic filler when the inorganic filler is recovered by dissolving the polyamide resin composition into hexafluoroisopropanol is at least 4 g/m2 per unit surface area of the inorganic filler measured by a BET method.